Chest X-ray screening is an important procedure for the detection and monitoring of lung abnormalities and diseases at an early stage in the lungs of patients. Medical personnel, such as doctors or radiologists, detect abnormalities directly from X-ray images. Assessing the image quality directly after acquisition is the task of a medical imaging professional. The image is checked as being of sufficient quality before the patient leaves the examination room. If the chest X-ray image is not of sufficient quality, a new image should be taken before the patient leaves the examination room. Image quality is dependent upon the skill of the system operator, ensuring that pre-defined standard operating procedures are followed. In particular, factors relating to patient positioning with respect to the detector require the patient's cooperation. U.S. 2004/0161141 discusses a method for deducing the orientation of a radiographic image from the digital representation of the image. Such systems can, however, be further improved.